Many processing systems and instruments include one or more vacuum chambers. One example is a Fourier Transform Mass Spectrometer (FTMS) system which includes two vacuum chambers connected through an orifice. One vacuum chamber operates at relatively high vacuum, e.g. 10−10 Torr, and the other vacuum chamber operates at relatively low vacuum, e.g. 10−4 Torr. The orifice is provided with a shutter that separates the low vacuum region from the high vacuum region. The shutter is opened for brief periods, typically a fraction of a second, to allow transport of ions from the low vacuum chamber to the high vacuum chamber for analysis. The shutter may operate at frequent intervals, e.g. once every half second.
One requirement of systems which include a high vacuum chamber is to maintain the ultrahigh vacuum (ultralow pressure) continuously without venting or significant pressure increases. When the high vacuum chamber is vented or gas leaks into the high vacuum chamber and causes a rise in pressure, the time to vacuum pump to the desired ultrahigh vacuum may be lengthy, resulting in expensive downtime of the entire system. For example, vacuum pumping a chamber from atmosphere to a pressure of 10−10 Torr may require on the order of two days. Accordingly, it is desirable to maintain the ultrahigh vacuum during maintenance and other operations which require venting of the low vacuum chamber.
A shutter may be used to provide brief access to the high vacuum chamber. Typical shutters are designed to open and close quickly and to operate reliably over extended periods. However, shutters which meet these requirements are not equipped with high vacuum seals. Therefore, such shutters permit leakage of gas into the high vacuum chamber, particularly when the low vacuum chamber is vented to atmosphere.
Accordingly, there is a need for improved methods and apparatus for isolating a high vacuum chamber from a low vacuum chamber or from atmosphere during operation and maintenance.